Keuchel (4-0, 1.22 ERA) has looked like the southpaw ace who won the 2015 AL Cy Young award, but Astros manager A.J. Hinch insisted the pairings are not rigidly defined. He alluded to schedule changes. A rainout on April 16 in Oakland jostled the rotation.

"I'm not going to have the personal catcher every single time," Hinch said before Friday's game against the Athletics, in which Gattis would receive Morton for the fifth time.

Unlike Keuchel, Morton (1-2, 4.29 ERA) consistently has labored in and out of jams in three of his four starts. Still, Hinch explained his choice for catcher depends more on lineup configurations.

"McCann's going to catch Morton eventually," Hinch said. "Keuchel is eventually, probably, going to have to pitch to Gattis."

Both catchers have made Hinch "completely comfortable" picking either to start. They have hit similarly well through 22 games. Gattis, a fifth-year righty with more gap power than McCann, is hitting .289 with two home runs and 11 runs batted in. McCann, a left-handed pull hitter, in his 13th season, is batting .279, with three home runs and 11 runs batted in.

Several teams in baseball likely would bat Gattis or McCann in the heart of their lineups because of their tape-measure shot capabilities. Hinch has the luxury of a deep lineup.

"That's a great strength of ours to have," Hinch said. "Two close to middle-of-the-order bats to choose from behind the plate."